Iron Blues

Direct prussian blues

A)

Process consists in oxidating a ferrous sulphate solution using air as oxidizing agent and a proper amount of sulphuric acid, since FeSO4 should turn into Fe2(SO4)3 it needs two more SO4 groups.

Sodium or Potasium Ferrocyanide is added. At the beginning the precipitate is white ("berlin white")or light blue, deepening in color as oxidation proceeds. Reaction is complete when the compound formed has turned deep blue.

B)

Using Manganese dioxide as the oxidizing agent.

C) Ammoniacal Blue

At the first step "berlin white" is obtained making react ferrous sulphate and potasium or sodium ferrocyanide in the presence of ammonium sulphate.

Then this "berlin white" is oxidized to obtain the ammonical blue. This kind of Iron Blue is the most common one.

D) High Hiding Strength Iron Blue

Now, if we want to obtain a high hiding strength iron blue, we have to use as raw material an iron yellow -freshly obtained or not-and to make it react with sodium or potasium ferrocyanide at boiling temperature and with an excess of sulphuric acid.

In the following case it has been used a suspension of Fe2O3 with a concentration of 184 grams per liter of iron yellow (Fe2O3.H2O)

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